The fraction of radiation absorbed in the canopy depends on the amount
and angular distribution of the solar irradiance reaching the top of the canopy
as well as the fraction of this irradiance that is transmitted through the canopy
gaps and reflected back to the vegetation by the background. This contribution
shows that the presence of snow on forest floors enhances the fraction
of absorbed Photosynthetically Active Radiation (PAR). A global analysis
of satellite-derived products reveals that this enhancement affects evergreen
and deciduous forests of the boreal zone. This snow-related effect may
usefully contribute to the photosynthesis process in evergreen forests especially
during spring time when radiation conditions are marginal but other
physiological constraints (such as temperature) permit the necessary biochemical
functions to take place.